The microplate is one of the most widely used reaction vessels in, for instance, analytical research and clinical diagnostics. Its main dimensions are defined in the standards of the American National Standards Institute (ANSI), based on an initiative from 1996 of the Society for Biomolecular Sciences (SBS). The most commonly used microplates have 96 (8×12) and 384 (16×24) wells, reagents and samples being dispensed into these wells either by manual pipetting or using automatic liquid dispensers.
The location of the wells on the plate is indicated with a two-character code, the first character being a letter indicating the row and the second character being a digit indicating the column of the well. For instance for a plate with 96 wells, the location code of the well at the upper left corner is A1 while that of the lower right corner is H12.
Manual pipetting is either carried out with a single channel pipette or a multiple channel pipette with 8 or 12 channels, particularly developed for rapid filling of the plate. During manual pipetting, it may be difficult to observe the liquid if the amount to be dispensed is small, or the liquid is colourless. This fact makes it difficult for the person using the pipette to observe which well has already received a sample and which well should be the next to receive one.
At present, all solutions for aiding in pipetting to microplates are separate devices on which the microplate is placed (so-called microplate illuminators or microplate trackers), which devices emit light through the bottom of the microplate, thus indicating to the user the specific well which should next receive a pipetted sample. Once the sample is pipetted, the user either presses a button or a pedal on the apparatus, thus causing the beam of light to move to the next well to receive a pipetted sample. In addition to such electronic devices, there are also manually operated devices allowing the user to mark the well which is the target for next pipetting, using indicators such as pegs to be placed on the edges of the microplate. The problem in the use of both these systems is the obvious risk for mistakes. The user may accidentally press the button or move the peg to the wrong location, or forget to press the button or move the pegs. Moreover, the user must obtain a separate device which takes up space on the working table. These disadvantages may be eliminated by the guidance device of the invention.